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vulkan: use scalar FA rather than coopmat2 when N==1 #13554

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Merged
0cc4m merged 1 commit into from
May 17, 2025
Merged

vulkan: use scalar FA rather than coopmat2 when N==1 #13554

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7 changes: 7 additions & 0 deletions ggml/src/ggml-vulkan/ggml-vulkan.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5872,10 +5872,17 @@ static void ggml_vk_flash_attn(ggml_backend_vk_context * ctx, vk_context& subctx
vk_pipeline *pipelines;
bool small_rows = N <= get_fa_num_small_rows(path);

// coopmat1 does not actually support "small rows" (it needs 16 rows).
// So use scalar instead.
if (small_rows && path == FA_COOPMAT1) {
path = FA_SCALAR;
}

// scalar is faster than coopmat2 when N==1
if (N == 1 && path == FA_COOPMAT2) {
path = FA_SCALAR;
}

bool f32acc = path == FA_SCALAR || dst->op_params[3] == GGML_PREC_F32;

switch (path) {
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